Capping layer over FET FeRAM to increase charge mobility

ABSTRACT

In some embodiments, the present disclosure relates to an integrated chip that includes a gate electrode over a substrate, and a gate dielectric layer arranged over the gate electrode. The gate dielectric layer includes a ferroelectric material. An active structure is arranged over the gate dielectric layer and includes a semiconductor material. A source contact and a drain contact are arranged over the active structure. A capping structure is arranged between the source and drain contacts and over the active structure. The capping structure includes a first metal material.

BACKGROUND

Many modern day electronic devices include non-volatile memory.Non-volatile memory is electronic memory that is able to store data inthe absence of power. A promising candidate for the next generation ofnon-volatile memory is ferroelectric random-access memory (FeRAM). FeRAMhas a relatively simple structure and is compatible with complementarymetal-oxide-semiconductor (CMOS) logic and thin film transistorfabrication processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of a fieldeffect transistor (FET) ferroelectric random access memory (FeRAM)device comprising a capping structure arranged over an active structure,wherein a bottommost layer of the active structure comprises a cocktaillayer.

FIG. 2 illustrates a magnified, cross-sectional view of some embodimentsof the microstructure of the cocktail layer.

FIG. 3 illustrates a cross-sectional view of some alternativeembodiments of a FET FeRAM device comprising a capping structurearranged over an active structure, wherein a bottommost layer of theactive structure comprises a cocktail layer.

FIGS. 4 and 5 illustrate cross-sectional views of some embodiments ofFET FeRAM devices comprising capping structures arranged over activestructures.

FIG. 6 illustrates a cross-sectional view of some embodiments of anintegrated chip comprising a FET FeRAM device having a capping structurearranged over an active structure and embedded within an interconnectstructure.

FIGS. 7-20 illustrate various views and schematics of some embodimentsof methods of forming a capping structure over an active structure of aFET FeRAM device.

FIG. 21 illustrates a flow diagram of some embodiments of a method offorming a capping structure over an active structure of a FET FeRAMdevice that corresponds to the methods of FIGS. 6-20 .

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

A thin film transistor (TFT) is a type of field effect transistor (FET)that includes an active structure that may be turned “ON” such thatmobile charge carriers flow through the active structure when asufficient signal (e.g., voltage, current) is applied to source contact,drain contact, and gate electrode of the TFT. In some instances, theactive structure comprises a semiconductor material that is transparentsuch as, for example, indium gallium zinc oxide (IGZO), amorphoussilicon, or some other suitable material for use in opticalapplications. In a bottom gate TFT, the gate electrode is arranged belowthe active structure and the source and drain contacts are arranged overthe active structure. A gate dielectric layer may separate the gateelectrode from the active structure. In some instances, the gatedielectric layer comprises a ferroelectric material, such that the TFTfunctions as a FET ferroelectric random access memory (FeRAM). Theferroelectric layer can store data values based on a process ofreversible switching between polarizations states because theferroelectric's crystal structure changes when an electric field ispresent.

To form a FET FeRAM device, a ferroelectric layer is formed over a gateelectrode. Then, an active structure is formed over the ferroelectriclayer, and source and drain contacts are formed over the activestructure. In some embodiments, depending on which materials of theactive structure directly contact the gate dielectric layer, defects maybe present at an interface the active structure and the gate dielectriclayer such as, for example, oxygen vacancies and surface states (i.e.,excess charges) which may reduce charge mobility in the activestructure. Further, defects may form at a topmost surface of the activestructure due to the topmost surfaces exposure to air in the surroundingenvironment. Such defects at the topmost surface of the active structuremay also include oxygen vacancies and surface states which increaseelectron scattering and reduce charge mobility.

Various embodiments of the present disclosure relate to forming acapping structure over the active structure and between source and draincontacts to reduce defects at the topmost surface of the activestructure and increase charge mobility of the active structure therebyimproving performance of the overall FET FeRAM device. In some suchembodiments, a topmost layer of the active structure comprises a firstmetal oxide material having a high bonding energy which reduces oxygenvacancies at the topmost surface of the active structure. Further, thecapping structure comprises, in some embodiments, one or more metalmaterials that have a strong ability to oxidize which reduces oxygenvacancies at the topmost surface of the active structure. Further, insome embodiments, a bottommost layer of the active structure maycomprise a mixture of the first metal oxide material and a second metaloxide material such that the first and second metal oxide materialsdirectly contact the ferroelectric layer to increase charge mobility andreduce surface states at an interface between the active structure andthe ferroelectric layer. With a reduction in defects (e.g., oxygenvacancies, surface states, weakly bonded oxygen) in the activestructure, the charge mobility in the active structure increases, whichincreases switching speeds and reliability of the FET FeRAM device.

FIG. 1 illustrates a cross-sectional view 100 of some embodiments of afield effect transistor (FET) ferroelectric random access memory (FeRAM)device comprising a capping structure arranged over an active structure.

The cross-sectional view 100 of FIG. 1 includes a gate electrode 106arranged over a substrate 102. In some embodiments, a dielectric layer104 is arranged between the gate electrode 106 and the substrate 102. Insome embodiments, a gate dielectric layer 108 is arranged over the gateelectrode 106. In such embodiments, the gate dielectric layer 108comprises a ferroelectric material that is configured to store datastates by changing crystal structure orientations and thus, resistancesupon exposure to different voltage biases.

In some embodiments, an active structure 110 is arranged over the gatedielectric layer 108. In some embodiments, the active structure 110comprises a semiconductor material that can be turned “ON” to form achannel region of mobile charge carriers when a sufficient voltage biasis applied across the active structure 110. The channel region of mobilecharge carriers can be controlled to read data from or write data to thegate dielectric layer 108. In some embodiments, a bottommost layer 110 bof the active structure 110 comprises a cocktail layer 112 comprising amixture of first and second materials, and a first active layer 114comprising a third material different than the first and secondmaterials is arranged over the cocktail layer 112. In some embodiments,the active structure 110 comprises a stack of the cocktail layers 112and the first active layers 114 in alternating order.

In some embodiments, source/drain contacts 118 are arranged over theactive structure 110. In some embodiments, the source/drain contacts 118are arranged within and extend through an interconnect dielectric layer116 to contact the topmost layer 110 t of the active structure 110.

In some embodiments, the first, second, and third materials of theactive structure 110 are metal-oxides. In some embodiments, the thirdmaterial of the first active layer 114 comprises a more crystallinematerial than the first and second materials. Thus, the first activelayer 114 is spaced apart from the gate dielectric layer 108 becauseotherwise, an interface between the third material of the first activelayer 114 and the gate dielectric layer 108 would be too rough and havepotential adhesion and structural issues on the gate dielectric layer108. In some embodiments, the first material of the cocktail layer 112comprises a stronger or more negative bonding energy than the secondmaterial. In some embodiments, the bonding energy may be determined froma metal oxide Ellingham diagram, which illustrates the Gibbs free energyof formation versus temperature for various metal-oxides.

Because the first material has a stronger bonding energy, less defects(e.g., oxygen vacancies) and thus, less surface states (i.e., excesscharges) are present at an interface between the first material of thecocktail layer 112 and the gate dielectric layer 108. In someembodiments, the second material of the cocktail layer 112 has a highermobility than the first material of the cocktail layer 112 due to aweaker bond energy and an increase in metal ions in the second material.Thus, mobile charge carriers may have a higher mobility at an interfacebetween the second material of the cocktail layer 112 and the gatedielectric layer 108. For these reasons, in some embodiments, thecocktail layer 112 comprises a mixture of the first and second materialsto reduce defects but also increase charge mobility at an interfacebetween the bottommost layer 110 b of the active structure 110 and thegate dielectric layer 108 to increase the reliability and switchingspeeds of the FET FeRAM device.

In some embodiments, a topmost layer 110 t of the active structure 110comprises a second active layer 120 comprising the first material andnot the second or third materials because of the high bonding energy ofthe first material. In some such embodiments, the high bonding energy ofthe first material reduces defects such as oxygen vacancies at a topmostsurface 110 s of the active structure 110. In some embodiments, thetopmost layer 110 t of the active structure 110 is arranged directly onone of the cocktail layers 112. Further, a capping structure 122 isarranged over the active structure 110 and between the source/draincontacts 118 to reduce defects (e.g., surface states, oxygen vacancies)at the topmost surface 110 s of the active structure 110. In someembodiments, the capping structure 122 extends through the interconnectdielectric layer 116 to contact the active structure 110.

In some embodiments, the capping structure 122 comprises a first metallayer 124 comprising a first metal material. In some embodiments, thefirst metal material of the first metal layer 124 comprises one or moremetals that has a strong oxidation ability. In other words, the firstmetal material has a high affinity for oxygen. In some embodiments, theaffinity for oxygen may be determined from a metal oxide Ellinghamdiagram, which illustrates the Gibbs free energy of formation versustemperature for various metal oxides; a metal oxide with a more negativeGibbs free energy indicates that the metal has a higher affinity foroxygen. In some embodiments, the Gibbs free energy may be measured byx-ray photoluminescence spectra, x-ray fluorescence, photoluminescence,or some other suitable measuring technique.

In some embodiments, the first metal layer 124 has a higher affinity foroxygen, or a more negative Gibbs free energy on an Ellingham diagram,than the metal-oxide materials of the active structure 110. Thus, whenthe first metal layer 124 is formed directly on the topmost layer 110 tof the active structure 110, the first metal material may diffuse intothe active structure 110 and bond with weakly bonded oxygen of theactive structure 110 to reduce defects (e.g., oxygen vacancies, surfacestates, weakly bonded oxygen) in the active structure 110 and increasecharge mobility in the active structure 110. In some such embodiments, adiffusion region 128 may be arranged in an upper area of the activestructure 110 and below the first metal layer 124 of the cappingstructure 122 that comprises the first metal material bonded withoxygen.

Therefore, in some embodiments, the capping structure 122 reducesdefects (e.g., oxygen vacancies, surface states, weakly bonded oxygen)near the topmost surface 110 s of the active structure 110 to increasecharge mobility of the active structure 110 thereby increasing switchingspeeds of the overall FET FeRAM device. With an increase in switchingspeeds, the FET FeRAM device may be turned “ON” quicker because mobilecharge carriers may move through the active structure easier. As aresult, data may be stored onto or read from the gate dielectric layer108 more easily and reliably.

FIG. 2 illustrates a magnified, cross-sectional view 200 of someembodiments of the microstructure of the cocktail layer. In someembodiments, the cross-sectional view 200 corresponds to box A of FIG. 1.

As shown in cross-sectional view 200, in some embodiments, the cocktaillayer 112 comprises first material regions 202 and second materialregions 204. In some embodiments, the second material regions 204 appearto be embedded within the first material regions 202. In otherembodiments, the first material regions 202 may appear to be embeddedwithin the second material regions 204. Nevertheless, in someembodiments, the cocktail layer 112 includes a mixture of the first andsecond materials, and the magnified, cross-sectional view 200 mayexhibit defined first material regions 202 comprising the first materialand second material regions 204 comprising the second material.

In some embodiments, the first material comprises gallium oxide, hafniumoxide, zirconium oxide, titanium oxide, aluminum oxide, tantalum oxide,strontium oxide, barium oxide, scandium oxide, magnesium oxide,lanthanum oxide, gadolinium oxide, or some other suitable metal oxide.In some embodiments, the second material comprises indium oxide, tinoxide, arsenic oxide, zinc oxide, or the like. In some embodiments, thethird material comprises zinc oxide. Thus, for example, in someembodiments, the first material comprises gallium oxide; the secondmaterial comprises indium oxide; and the third material comprises zincoxide, such that the active structure (110 of FIG. 1 ) comprises indiumgallium zinc oxide (IGZO), which is a semiconducting material. In someother embodiments, the active structure (110 of FIG. 1 ) may comprisetin gallium zinc oxide, indium hafnium zinc oxide, or some othersuitable combination of the first, second, and third materials thattogether form a semiconducting material.

In some such embodiments, the first material regions 202 aresubstantially amorphous, and the second material regions 204 aresubstantially amorphous. With the first and second material regions 202,204 being amorphous, roughness and electron scattering are reduced atthe interface between the cocktail layer 112 and the gate dielectriclayer (108 of FIG. 1 ). Further in some embodiments, because the firstmaterial regions 202 and the second material regions 204 directlycontact the gate dielectric layer (108 of FIG. 1 ), defects are reducedand charge mobility is increased which increases the “ON” current andthe switching speeds of the FET FeRAM device.

FIG. 3 illustrates a cross-sectional view 300 of some alternativeembodiments of a FET FeRAM device comprising a capping structure over anactive structure.

In some embodiments, the substrate 102 comprises a silicon on insulatorsubstrate such that the dielectric layer 104 is arranged between a bulksubstrate layer 302 and an active substrate layer 304. In someembodiments, the topmost layer 110 t of the active structure 110 isarranged directly on one of the first active layers 114. It will beappreciated that the active structure 110 may comprise more or lesslayers than what is illustrated in FIG. 3A.

In some embodiments, the gate dielectric layer 108 has a first thicknesst₁ in a range of between, for example, approximately 5 nanometers andapproximately 20 nanometers. In some embodiments, the active structure110 may have a second thickness t₂ in a range of between, for example,approximately 5 nanometers and approximately 15 nanometers. In someembodiments, each cocktail layer 112, first active layer 114, and/orsecond active layer 120 has a third thickness t₃ in a range of between,for example, approximately 0.1 angstroms to approximately 500 angstroms.In some embodiments, a ratio of the first material to the secondmaterial ranges from approximately 0.1 to approximately 0.99 in thecocktail layer 112.

In some embodiments, the gate electrode 106 may comprise, for example,titanium nitride, aluminum, tungsten, copper, or some other suitableconductive material. In some embodiments, the gate dielectric layer 108comprises a ferroelectric material such as, for example, strontiumbismuth tantalite, lead zirconate titanate, hafnium zinc oxide, hafniumzirconium oxide, doped hafnium oxide, or the like. In some embodiments,the gate electrode 106 may have a thickness in a range of between, forexample, approximately 10 nanometers and approximately 20 nanometers. Insome embodiments, the source/drain contacts 118 may comprise, forexample, aluminum, tungsten, copper, tantalum, titanium, or some othersuitable conductive material.

Further, in some embodiments, the capping structure 122 comprisesaluminum, calcium, scandium, yttrium, niobium, tantalum, chromium, iron,titanium, silicon, hafnium, zirconium, titanium, strontium, barium,magnesium, lanthanum, gadolinium, a combination thereof, and/or someother suitable metal or semiconductor material with a strong oxidationability (i.e., a high affinity for oxygen). In some embodiments, thecapping structure 122 has a thickness in a range of between, forexample, approximately 0.1 angstroms to approximately 30 angstroms. Insome embodiments, the capping structure 122 further comprises a secondmetal layer 326 comprising a second metal material that is differentthan the first metal material of the first metal layer 124. For example,in some embodiments, the first metal layer 124 may comprise calcium, andthe second metal layer 326 may comprise aluminum. In some suchembodiments, the diffusion region 128 of the active structure 110 maycomprise calcium oxide. In some embodiments, the first metal layer 124is a single layer formed by atomic layer deposition (ALD). In some otherembodiments, the first metal layer 124 comprises multiple layers of asame material formed by ALD. In some embodiments, the second metal layer326 is a single layer formed by atomic layer deposition (ALD). In someother embodiments, the second metal layer 326 comprises multiple layersof a same material formed by ALD. Nevertheless, in some embodiments, thecapping structure 122 comprises one or more metal materials arranged aslayers and/or as alloys that directly contact the topmost surface 110 sof the active structure 110 to reduce defects (e.g., oxygen vacancies,surface states, weakly bonded oxygen) of the active structure 110 andimprove performance of the FET FeRAM device.

FIG. 4 illustrates a cross-sectional view 400 of some other embodimentsof a FET FeRAM device comprising a capping structure over an activestructure.

In some embodiments, the active structure 110 comprises a mixture of thefirst, second, and third materials over the substrate 102. Thus, in someembodiments, the active structure 110 comprises a lower portion 402 thatdoes not have defined layers. In some other embodiments, the lowerportion 402 may comprise a single semiconductor material such assilicon, for example. In some embodiments, the second active layer 120is arranged directly on the lower portion 402 of the active structure110 and comprises the first material. In some embodiments, the lowerportion 402 is arranged directly on the gate dielectric layer 108. Inyet some other embodiments, the cocktail layer (112 of FIG. 1 ) may bearranged directly between the lower portion 402 of the active structure110 and the gate dielectric layer 108.

In some embodiments, the diffusion region 128 of the active structure110 extends below the topmost layer 110 t of the active structure 110.In some other embodiments, the diffusion region 128 extends into thetopmost layer 110 t of the active structure 110 but does not extendbelow the topmost layer 110 t of the active structure 110 (see, e.g.,FIG. 3 ).

Further, in some embodiments, a topmost surface of the capping structure122 is narrower than a bottommost surface of the capping structure 122.In some such embodiments, the capping structure 122 may be formedthrough a deposition process followed by a patterning process, prior toforming the interconnect dielectric layer 116.

FIG. 5 illustrates a cross-sectional view 500 of yet some otherembodiments of a FET FeRAM device comprising a capping structure over anactive structure.

In some embodiments, the active structure 110 comprises a stack of firstactive layers 114, second active layers 120, and third active layers 502over the gate dielectric layer 108. In some such embodiments, thearrangement of the first, second, and third active layers 114, 120, 502may be, for example, the first active layer 114 arranged over the secondactive layer 120, and the third active layer 502 arranged over the firstactive layer 114. It will be appreciated that a different sequence ofthe first, second, and third active layers 114, 120, 502 than what isshown in FIG. 5 is also within the scope of this disclosure.

In some embodiments, the first active layers 114 may comprise the thirdmaterial, the second active layers 120 may comprise the first material,and the third active layers 502 may comprise the second material. Inother words, in some embodiments, none of the layers of the activestructure 110 comprise a mixture of metal oxides; instead each layer ofthe active structure 110 comprises a single metal oxide. In some otherembodiments, a bottommost layer 110 b of the active structure 110 maycomprise the cocktail layer (112 of FIG. 1 ) to increase charge mobilityat an interface between the active structure 110 and the gate dielectriclayer 108.

In some embodiments, the topmost layer 110 t of the active structure 110comprises the second active layer 120 which comprises the firstmaterial. In some embodiments, the topmost layer 110 t is arrangeddirectly on one of the first active layers 114 or directly on one of thethird active layers 502.

Further, in some embodiments, a topmost surface of the capping structure122 is wider than a bottommost surface of the capping structure 122. Insome such embodiments, the capping structure 122 may be formed through apatterning process followed by a deposition process after to forming theinterconnect dielectric layer 116.

FIG. 6 illustrates a cross-sectional view 600 of some embodiments of anintegrated chip comprising a FET FeRAM device embedded within aninterconnect structure.

In some embodiments, the FET FeRAM device is arranged within aninterconnect structure 602 that is arranged over the substrate 102. Insome such embodiments, the FET FeRAM devices (e.g., 604 a, 604 b) arearranged within the back-end-of-line (BEOL) portion of the integratedchip, wherein the BEOL portion of the integrated chip is arranged overthe front-end-of-line (FEOL) portion of the integrated chip. In someembodiments, the FET FeRAM devices (e.g., 604 a, 604 b) are electricallycoupled to devices in the FEOL portion of the integrated chip. In someembodiments, the FEOL portion of the integrated chip comprises at leastone transistor device arranged within and/or over the substrate 102 suchas, for example, a metal-oxide-semiconductor field effect transistor(MOSFET), a fin field effect transistor (finFET), a gate all aroundfield effect transistor (GAAFET), or some other type of transistordevice.

In some embodiments, the interconnect structure 602 comprisesinterconnect contacts 618 and interconnect wires 608 disposed withininterconnect dielectric layers 116 and etch stop layers 606. In someembodiments, the interconnect contacts 618 and the interconnect wires608 may comprise, for example, aluminum, tungsten, copper, tantalum,titanium, or some other suitable conductive material. In someembodiments, the interconnect dielectric layers 116 may comprise, forexample, a nitride (e.g., silicon nitride, silicon oxynitride), acarbide (e.g., silicon carbide), an oxide (e.g., silicon oxide),borosilicate glass (BSG), phosphoric silicate glass (PSG),borophosphosilicate glass (BPSG), a low-k oxide (e.g., a carbon dopedoxide, SiCOH), or the like. In some embodiments, the etch stop layers606 may comprise, for example, silicon carbide, silicon nitride, or someother suitable dielectric material.

As shown in FIG. 6 , a first FET FeRAM 604 a and a second FET FeRAM 604b arranged within the interconnect structure 602. In some embodiments,the interconnect contacts 618 are arranged over and coupled to theactive structure 110 such that the interconnect contacts 618 serve asthe source/drain contacts (118 of FIG. 5 ) of the FET FeRAM device. Insome embodiments, as shown with the first FET FeRAM 604 a, the gateelectrode 106 is arranged over one of the interconnect wires 608. Inother embodiments, the gate electrode 106 may be arranged over one ofthe interconnect contacts 618. In some embodiments, as shown with thesecond FET FeRAM 604 b, the gate electrode 106 is omitted, and instead,the gate dielectric layer 108 is arranged directly on one of theinterconnect wires 608 of the interconnect structure 602.

In some embodiments, the capping structure 122 is not directly coupledto one of the interconnect wires 608 or interconnect contacts 618. Insome other embodiments, the capping structure 122 may be coupled to aninterconnect wire 608 or an interconnect contact 618 to ground thecapping structure 122. In some such other embodiments, grounding thecapping structure 122 may improve the gate dielectric layer's 108ability to switch between polarization states to store memory.

In some embodiments, due to the small vertical dimensions of the FETFeRAMs (e.g., 604, 604 b), the FET FeRAMs may be integrated into theinterconnect structure 602 of an integrated chip and controlled by thenetwork of interconnect wires 608 and interconnect contacts 618 of theinterconnect structure 602 to store data within the gate dielectriclayers 108.

FIGS. 7-21 illustrate various schematics and cross-sectional views700-2100 of some embodiments of a method of forming a FET FeRAM devicecomprising a capping structure arranged over an active structure toreduce defects in the active structure and increase switching speeds andreliability of the overall FET FeRAM device. Although FIGS. 7-21 aredescribed in relation to a method, it will be appreciated that thestructures disclosed in FIGS. 7-21 are not limited to such a method, butinstead may stand alone as structures independent of the method.

As shown in cross-sectional view 700 of FIG. 7 , in some embodiments, agate electrode 106 is formed over a substrate 102. In variousembodiments, the substrate 102 may comprise any type of semiconductorbody (e.g., silicon/CMOS bulk, SiGe, SOI, etc.) such as a semiconductorwafer or one or more die on a wafer, as well as any other type ofsemiconductor and/or epitaxial layers formed thereon and/or otherwiseassociated therewith. In some other embodiments, the substrate 102 maycomprise a support transparent material, such as a glass, for use inoptical applications. In the cross-sectional view 700 of FIG. 7 , thesubstrate 102 is a silicon-on-insulator (SOI) substrate comprising adielectric layer 104 arranged over a bulk substrate layer 302 andarranged below an active substrate layer 304. In some such embodiments,the bulk substrate layer 302 and the active substrate layer 304 maycomprise, for example, silicon, germanium, or some other suitablesemiconductor material. In some embodiments, the dielectric layer 104comprises silicon dioxide, silicon oxynitride, or some other suitabledielectric layer.

In some embodiments, the gate electrode 106 is formed over the substrate102 by way of a deposition process (e.g., physical vapor deposition(PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD),direct current sputtering, etc.). In some embodiments, the gateelectrode 106 comprises titanium nitride, aluminum, tungsten, copper, orsome other suitable conductive material. In some embodiments, the gateelectrode 106 is formed to have a thickness in a range of between, forexample, approximately 10 nanometers and approximately 20 nanometers.

As shown in cross-sectional view 800 of FIG. 8 , in some embodiments, agate dielectric layer 108 is formed over the gate electrode 106. In someembodiments, the gate dielectric layer 108 is formed by atomic layerdeposition in a chamber at a temperature in a range of between, forexample, approximately 200 degrees Celsius and approximately 400 degreesCelsius. In some other embodiments, the gate dielectric layer 108 isformed by way of another deposition process (e.g., PVD, CVD, etc.). Insome embodiments, the gate dielectric layer 108 comprises aferroelectric material such as, for example, strontium bismuthtantalite, lead zirconate titanate, hafnium zinc oxide, hafniumzirconium oxide, doped hafnium oxide, or the like. For example, in someembodiments, the gate dielectric layer 108 comprises hafnium zirconiumoxide, wherein an atomic ratio between hafnium and zirconium isapproximately one to one. In some embodiments, the gate dielectric layer108 has a first thickness t₁ that is in a range of between approximately5 nanometers and approximately 20 nanometers.

As shown in cross-sectional view 900 of FIG. 9 , in some embodiments,the substrate 102 is transferred onto a wafer chuck 901 within areaction chamber defined by chamber housing 902. In some embodiments,the reaction chamber is an atomic layer deposition (ALD) chamber, lowpressure vessel, and/or the like. In some embodiments, the substrate 102was already in the reaction chamber during the formation of the gateelectrode 106 and/or gate dielectric layer 108 forming in FIGS. 7 and 8, respectively. In some embodiments, a first gas inlet line 908 passesthrough the chamber housing 902 such that precursor vessels defined byvessel housings (e.g., 910, 918, 932) are coupled to the reactionchamber through the first gas inlet line 908. In some embodiments, asecond gas inlet line 914 passes through the chamber housing 902 suchthat an oxygen source 916 can enter the reaction chamber. In someembodiments, a gas outlet line 919 passes through the chamber housing902 such that various gases can exit the reaction chamber duringdeposition processes.

In some embodiments, a first precursor vessel defined by a first vesselhousing 910, a second precursor vessel defined by a second vesselhousing 918, and a third precursor vessel defined by a third vesselhousing 932 are coupled to the first gas inlet line 908 and to an inertgas source 912. In other embodiments, more or less than three precursorvessels may be coupled to the reaction chamber. In some embodiments, theinert gas source 912 may be turned “ON” such that inert gas enters oneor more of the precursor vessels to activate precursors in eachprecursor vessel such that a precursor vapor enters the reaction chamberthrough the first gas inlet line 908 to form a layer on the gatedielectric layer 108. In some embodiments, each precursor vesselcomprises door structures 936 that may be controlled by controlcircuitry to be opened or closed, as indicated by arrows 934, torespectively allow or prohibit the inert gas from the inert gas source912 to enter the precursor vessel.

In some embodiments, the first precursor vessel comprises a firstprecursor plate 920 that holds a first solid precursor 922 withingrooves of the first precursor plate 920. In some embodiments, thesecond precursor vessel comprises a second precursor plate 924 thatholds a second solid precursor 926 within grooves of the secondprecursor plate 924. In some embodiments, the third precursor vesselcomprises a third precursor plate 928 that holds a third solid precursor930 within grooves of the third precursor plate 928. In someembodiments, the first, second, and third solid precursors 922, 926, 930each comprise solid precursors corresponding to certain materials oflayers to be formed on the gate dielectric layer 108 to form an activestructure over the gate dielectric layer 108.

For example, in some embodiments, the active structure to be formed onthe gate dielectric layer 108 comprises a combination of first, second,and third materials. In some embodiments, the first solid precursor 922corresponds to the first material; the second solid precursor 926corresponds to the second material; and the third solid precursor 930corresponds to the third material. In other embodiments, the first solidprecursor 922 may correspond to a mixture of solid precursorscorresponding to the first and second materials; the second solidprecursor 926 may correspond to the first material; and the third solidprecursor 930 may correspond to the third material. In yet otherembodiments, the first solid precursor 922 may correspond to a mixtureof solid precursors corresponding to the first, second, and thirdmaterials; and the second solid precursor 926 may correspond to thefirst material; and the third solid precursor 930 may be omitted. In yetother embodiments, more than the three precursor vessels may be coupledto the chamber housing 902.

It will be appreciated that various methods may be used to form theactive structure over the gate dielectric layer 108, and each method mayutilize different combinations of solid precursors in the precursorvessels. FIGS. 10A-10C will correspond to first and second methods offorming the active structure over the gate dielectric layer 108; FIGS.11A and 11B will correspond to a third method of forming the activestructure over the gate dielectric layer 108; and FIGS. 12A and 12B willcorrespond to a fourth method of forming the active structure over thegate dielectric layer 108. Thus, the method may proceed from FIG. 9 toFIGS. 10A and 10B; from FIG. 9 to FIGS. 10A and 10C, thereby skippingFIG. 10B; from FIG. 9 to FIGS. 11A and 11B, thereby skipping FIGS.10A-10C; or from FIG. 9 to FIGS. 12A and 12B, thereby skipping FIGS.10A-11B.

Further, the methods in FIGS. 10A-12B illustrate methods of forming theactive structure over the gate dielectric layer 108 by atomic layerdeposition (ALD). However, it will be appreciated that in otherembodiments, the active structure may be formed over the gate dielectriclayer 108 by other deposition methods such as, for example, CVD, PVD, orthe like.

As shown in cross-sectional view 1000A of FIG. 10A, in some embodiments,an atomic layer deposition process is performed to form an activestructure 110 over the gate dielectric layer 108, wherein the activestructure 110 comprises a stack of cocktail layers 112 comprising amixture of first and second materials and first active layers 114comprising a third material. In some such embodiments, a bottommostlayer 110 b of the active structure 110 comprises one of the cocktaillayers 112. Further, in some embodiments, a topmost layer 110 t of theactive structure 110 comprises a second active layer 120 comprising thefirst material, but not the second or third materials.

In some such embodiments, the first, second, and third materials of theactive structure 110 are metal oxides. In some such embodiments, thefirst, second, and third solid precursors 922, 926, 930 may comprise afirst metal, a second metal, and a third metal, respectively,corresponding to the first, second, and third materials of the activestructure 110. For example, in some embodiments, the first material maycomprise gallium, hafnium, zirconium, titanium, aluminum, tantalum,strontium, barium, scandium, magnesium, lanthanum, gadolinium, or someother suitable metal. In some embodiments, wherein the first materialcomprises gallium, the first precursor of the first solid precursor 922may comprise, for example, Ga(C₂H₅)₃, Ga(NMe)₃, Ga(C₅H₇O₂)₃, GaCp*,Ga(CH₃)₃, Ga₂(NMe₂)₆, or some other suitable solid precursor comprisinggallium.

In some embodiments, the second material comprises indium, tin, zinc,arsenic, or some other suitable metal. In some such embodiments, whereinthe second material comprises indium, the second solid precursor 926 maycomprise, for example, trimethyl-indium, triethyl-indium, InCp(C₅H₅In),InCA-1(C₈H₂₄InNSi₂), DADI(C₇H₁₈InN), or some other suitable solidprecursor comprising indium. In some other embodiments, the thirdmaterial comprises zinc or some other metal. In some embodiments, thethird solid precursor 930 comprises, for example, Zn(CH₃COO)₂,diethylzinc, dimethylzinc, zinc acetate, (CH₃)Zn(OCH(CH₃)₂), or someother suitable solid precursor.

FIG. 10B illustrates a timing diagram 1000B of some embodiments of afirst method of forming the active structure 110 over the gatedielectric layer 108, wherein the first solid precursor 922 correspondsto a first material; the second solid precursor 926 corresponds to asecond material; and the third solid precursor 930 corresponds to athird material. FIG. 10B will be described in conjunction with thecross-sectional view 1000A of FIG. 10A.

In some embodiments, to form the active structure 110, first, a cocktaillayer 112 is formed over the gate dielectric layer 108. In some suchembodiments, the cocktail layer 112 comprises a mixture of the first andsecond materials. Thus, in some embodiments, step one 1004 of the methodfirst comprises, according to the legend 1002 of FIG. 10B and the timingdiagram 1000B of FIG. 10B, activating the first solid precursor 922 andthe second solid precursor 926 at the same time. In some embodiments,the first and second solid precursors 922, 926 are activated by turningthe inert gas source 912 “ON.” Further, in some embodiments, the doorstructures 936 on the first and second vessel housings 910, 918 are“open” while the door structures 936 on the third vessel housing 932 are“closed” such that the inert gas from the inert gas source 912 entersand activates the first and second solid precursors 922, 926, and notthe third solid precursor 930. In some embodiments, the inert gas source912 comprises, for example, nitrogen gas, argon gas, hydrogen gas, acombination thereof, or some other suitable gas.

Further, in some embodiments, after the inert gas source 912 activatesthe first and second solid precursors 922, 926, the oxygen source 916 isturned “ON” in step two 1006 of the method such that an oxygen vapor isintroduced into the reaction chamber. In some embodiments, the oxygensource 916 may comprise water. In some such embodiments, the oxygenvapor from the oxygen source 916 reacts with a precursor mixture vaporfrom the first and second solid precursors 922, 926 in the reactionchamber to form the cocktail layer 112 on the gate dielectric layer 108by ALD. In some such embodiments, the cocktail layer 112 comprises amixture of first and second materials that are metal oxides.

In some embodiments, the third solid precursor 930 is then activated instep three 1008 of the method by closing the door structures 936 to thefirst and second vessel housings 910, 918, opening the door structures936 of the third vessel housing 932, and turning “ON” the inert gassource 912. In some such embodiments, the inert gas from the inert gassource 912 reacts with the third solid precursor 930 and a precursorvapor enters the reaction chamber. Then, in step four 1010 of the methodturns the oxygen source 916 “ON” such that oxygen vapor is introducedinto the reaction chamber. In some such embodiments, the oxygen vaporreacts with the precursor vapor from the third solid precursor 930 toform a first active layer 114 over the cocktail layer 112 by ALD. Insome embodiments, steps one through four 1004, 1006, 1008, 1010 arerepeated multiple times to form a stack of cocktail layers 112 and firstactive layers 114 over the gate dielectric layer 108.

In some embodiments, a topmost layer 110 t of the active structure 110comprises a second active layer 120 made up of the first material andnot the second or third materials. Thus, in some embodiments, the methodof FIG. 10B proceeds with step five 1012, wherein the door structures936 of the second and third vessel housings 918, 932 are closed, thedoor structures 936 of the first vessel housing 910 are opened, and theinert gas source 912 is turned “ON” to activate the first solidprecursor 922. Further, in step six 1014 of the method, the oxygensource 916 “ON” such that oxygen vapor is introduced into the reactionchamber. In some such embodiments, the oxygen vapor reacts with theprecursor vapor from the first solid precursor 922 to form the secondactive layer 120 over the cocktail layers 112 and first active layers114 by ALD.

In some embodiments, byproducts of the reactions between the precursorvapors and the oxygen vapor may exit the reaction chamber through thegas outlet line 919. In some embodiments, the gas pulses of steps onethrough six 1004, 1006, 1008, 1010, 1012, 1014 may each have a timeperiod in a range of between, for example, approximately 1 millisecondto approximately 20 minutes. Further, in some embodiments, the gaspulses of steps one through six 1004, 1006, 1008, 1010, 1012, 1014 donot overlap with one another, besides the activation of the first andsecond solid precursors 922, 926 in step one 1004. In some otherembodiments, the gas pulses of steps one through six 1004, 1006, 1008,1010, 1012, 1014 may partially overlap with one another. For example, insome other embodiments, step two 1006 may begin before the inert gassource 912 used in step one 1004 is completely turned “OFF.”

Because the first material of the cocktail layer 112 has a strongerbonding energy, less defects (e.g., oxygen vacancies) and thus, lesssurface states (i.e., excess charges) are present at an interfacebetween the first material of the cocktail layer 112 and the gatedielectric layer 108. In some embodiments, the second material of thecocktail layer 112 has a higher mobility than the first material of thecocktail layer 112 due to a weaker bond energy and an increase in metalions in the second material. Thus, mobile charge carriers may have ahigher mobility at an interface between the second material of thecocktail layer 112 and the gate dielectric layer 108. Therefore, thebottommost layer 110 b of the active structure 110 comprises thecocktail layer 112 which includes a mixture of the first and secondmaterials to reduce defects but also increase charge mobility at aninterface between the bottommost layer 110 b of the active structure 110and the gate dielectric layer 108.

Further, the second active layer 120 comprises the first material whichhas a higher bonding energy than the second and third materials. Byforming the second active layer 120 as the topmost layer 110 t of theactive structure 110, defects (e.g., surface states, oxygen vacancies)at a topmost surface of the active structure 110 are reduced.

FIG. 10C illustrates a timing diagram 1000C of some embodiments of asecond method of forming the active structure 110 over the gatedielectric layer 108, wherein the first solid precursor 922 correspondsto a precursor mixture of the first and second materials; the secondsolid precursor 926 corresponds to a first material; and the third solidprecursor 930 corresponds to a third material. FIG. 10C will bedescribed in conjunction with the cross-sectional view 1000A of FIG.10A.

In some other embodiments, the first solid precursor 922 corresponds toa mixture of precursors corresponding to the first and second materialsof the cocktail layer 112. In some embodiments, a ratio of a firstprecursor corresponding to the first material to a second precursorcorrespond to the second material is in a range of between, for example,approximately 0.01 and approximately 0.99. Thus, in some embodiments,step one 1004 of the method comprises activating the solid precursormixture in the first vessel housing 910 by opening the door structures936 of the first vessel housing 910, closing the door structures 936 ofthe second and third vessel housings 918, 932, and turning “ON” theinert gas source 912. Then, the inert gas of the inert gas source 912reacts with the solid precursor mixture such that a precursor mixturevapor enters the reaction chamber. In some embodiments, the method ofFIG. 10C proceeds with step two 1006, wherein the oxygen source 916 isturned “ON” such that an oxygen vapor reacts with the precursor mixturevapor in the reaction chamber to form the cocktail layer 112 on the gatedielectric layer 108 by ALD.

In some embodiments, steps three through six 1008, 1010, 1012, 1014comprise the same or similar steps as described with respect to themethod of FIG. 10B.

As shown in cross-sectional view 1100A of FIG. 11A, in some otherembodiments, the active structure 110 formed over the gate dielectriclayer 108 comprises a stack of first active layers 114 comprising thethird material, second active layers 120 comprising the first material,and third active layers 502 comprising the second material. In some suchembodiments, the bottommost layer 110 b of the active structure 110 maycomprise one of the first, second, or third active layers 114, 120, 502.In some embodiments, the topmost layer 110 t of the active structure 110comprises one of the second active layers 120 comprising the firstmaterial.

FIG. 11B illustrates a timing diagram 1100B of some embodiments of athird method of forming the active structure 110 over the gatedielectric layer 108 as shown in cross-sectional view 1100A of FIG. 11A,wherein the first solid precursor 922 in the first precursor vessel maycorrespond to the first material; the second solid precursor 926 in thesecond precursor vessel may correspond to the second material; and thethird solid precursor 930 may correspond to the third material. FIG. 11Bwill be described in conjunction with the cross-sectional view 1100A ofFIG. 11A.

As shown in the timing diagram 1100B, in some embodiments, step one 1104of the method includes turning “ON” the inert gas source 912 to activatethe first solid precursor 922 associated with the first material of oneof the second active layers 120. In some embodiments, step two 1106 ofthe method comprises turning on the oxygen source 916 such that anoxygen vapor reacts with a first precursor vapor from step one 1104 toform one of the second active layers 120 over the gate dielectric layer108 by ALD. In some embodiments, the method proceeds with step three1108, wherein the inert gas source 912 is turned on to activate thesecond solid precursor 926 associated with one of the third activelayers 502. In some embodiments, step four 1110 of the method comprisesturning on the oxygen source 916 such that an oxygen vapor reacts with asecond precursor vapor from step three 1108 to form one of the thirdactive layers 502 over one of the second active layers 120 by ALD.

In some embodiments, the method proceeds with step five 1112, whereinthe inert gas source 912 is turned “ON” to active the third solidprecursor 930 associated with the third material of one of the firstactive layers 114. In some embodiments, step six 1114 of the methodcomprises turning on the oxygen source 916 such that an oxygen vaporreacts with a third precursor vapor from step five 1112 to form one ofthe first active layers 114 over one of the third active layers 502 byALD. In some embodiments, steps one through six 1104, 1106, 1108, 1110,1112 are repeated to form a stack of first, second, and third activelayers 114, 120, 502 over the gate dielectric layer 108. Then, in someembodiments, the method of FIG. 11B comprises steps seven 1116 and eight1118 to form the topmost layer 110 t of the active structure 110comprising the second active layer 120. Thus, in some embodiments stepsseven 1116 and eight 1118 comprise the same or similar steps as stepsone 1104 and two 1106 to form a second active layer 120.

As shown in cross-sectional view 1200A of FIG. 12A, in some otherembodiments, the active structure 110 formed over the gate dielectriclayer 108 comprises a lower portion 402 that includes a mixture of thefirst, second, and third materials over the gate dielectric layer 108.Thus, in some embodiments, the active structure 110 comprises a lowerportion 402 that does not have defined layers. Further, in some suchother embodiments, a second active layer 120 comprising the firstmaterial is formed over the lower portion 402 such that the activestructure 110 comprises the second active layer 120 arranged over thelower portion 402.

FIG. 12B illustrates a timing diagram 1200B of some embodiments of afourth method of forming the active structure 110 over the gatedielectric layer 108 as shown in cross-sectional view 1200A of FIG. 12A,wherein the first solid precursor 922 in the first precursor vessel maycorrespond to the first material; the second solid precursor 926 in thesecond precursor vessel may correspond to the second material; and thethird solid precursor 930 may correspond to the third material. FIG. 12Bwill be described in conjunction with the cross-sectional view 1200A ofFIG. 12A.

As shown in the timing diagram 1200B of FIG. 12B, in some embodiments,step one 1204 of the method includes activating the first, second, andthird solid precursors 922, 926, 930 at a same time by turning the inertgas source 912 “ON.” Then, in step two 1206 of the method, the oxygensource 916 is turned “ON” such that an oxygen vapor reacts with aprecursor mixture vapor from step one 1204 to form the lower portion 402of the active structure 110 by ALD. In some embodiments, steps one 1204and two 1206 are repeated many times to increase a thickness of thelower portion 402. In some embodiments, after the formation of the lowerportion 402 of the active structure, the method proceeds with step three1208, wherein the inert gas source is turned “ON” to activate the firstsolid precursor 922, but not the second or third solid precursors 926,930. Further, in some embodiments, the method proceeds with step four1210, wherein the oxygen source 916 is turned “ON” such that an oxygenvapor reacts with a second mixture vapor from step three 1208 to formthe second active layer 120 over the lower portion 402 of the activestructure 110.

Therefore, FIGS. 10A-12B illustrate a variety of methods that may beused to form the active structure 110 over the gate dielectric layer108. It will be appreciated that other related methods and/orcombination of the methods of FIGS. 10A-12B are also within the scope ofthis disclosure.

In some embodiments, the method proceeds with forming a cappingstructure over the active structure. FIGS. 13-16 illustrate a firstmethod of forming a capping structure over the active structure 110,whereas FIGS. 17-20 illustrates a second method of forming a cappingstructure over the active structure 110. Thus, in some embodiments,after forming the active structure 110 over the gate dielectric layer108, the method may proceed to FIG. 13 or to FIG. 17 , thereby skippingthe steps in FIGS. 13-16 .

As shown in cross-sectional view 1300 of FIG. 13 , in some embodiments,a first continuous metal layer 1302 is formed over the active structure110. In some embodiments, the first continuous metal layer 1302comprises a first metal material that has a higher affinity for oxygenthan the metals in the active structure 110. Thus, in some embodiments,the first metal material is different than metals in the activestructure 110. In some embodiments, the first continuous metal layer1302 may comprise, for example, aluminum, calcium, scandium, yttrium,niobium, tantalum, chromium, iron, titanium, silicon, hafnium,zirconium, titanium, strontium, barium, magnesium, lanthanum,gadolinium, a combination thereof, and/or some other suitable metal orsemiconductor material with a strong oxidation ability (i.e., a highaffinity for oxygen). In some embodiments, the first continuous metallayer 1302 is formed using an atomic layer deposition (ALD) process, andthus, may be formed within a same ALD reaction chamber used for formingthe active structure 110. For example, in some embodiments, the firstcontinuous metal layer 1302 may be formed using an ALD process byactivating a precursor associated with the first metal material byturning “ON” an inert gas source (e.g., 912 of FIG. 9 ). In otherembodiments, the first continuous metal layer 1302 may be formed using adifferent deposition process than ALD, such as, for example, PVD, CVD,sputtering, or some other suitable process.

In some embodiments, when an ALD process is used to form the firstcontinuous metal layer 1302, if the first continuous metal layer 1302comprises aluminum, the precursor used may comprise, for example,Al(CH₃)₃ or some other precursor comprising aluminum. In someembodiments, when an ALD process is used to form the first continuousmetal layer 1302, if the first continuous metal layer 1302 comprisescalcium, the precursor used may comprise, for example,Ca(OCC(CH₃)₃CHCOC(CH₃)₃))₂, calcium bis (2, 2, 6, 6-tetramethyl-3,5-heptanedionate), or some other precursor comprising calcium.

In some embodiments, a second continuous metal layer 1304 is then formedover the first continuous metal layer 1302. In some embodiments, thesecond continuous metal layer 1304 may comprise a same or differentmaterial than the first continuous metal layer 1302. In otherembodiments, the second continuous metal layer 1304 is omitted. In someembodiments, the second continuous metal layer 1304 is formed using asame deposition process as the first continuous metal layer 1302 such asALD, PVD, CVD, sputtering, or the like. In some embodiments, the secondcontinuous metal layer 1304 may be formed using an ALD process byactivating a precursor associated with the second metal material byturning “ON” an inert gas source (e.g., 912 of FIG. 9 ). In someembodiments, a thickness of the first and second continuous metal layers1302, 1304 may be in a range of between, for example, approximately 0.1angstroms to approximately 30 angstroms.

As shown in cross-sectional view 1400 of FIG. 14 , in some embodiments,a masking structure 1402 is formed over the first and second continuousmetal layers 1302, 1304. In some embodiments, the masking structure 1402is formed using photolithography and removal (e.g., etching) processes.In some embodiments, the masking structure 1402 comprises a photoresistmaterial or a hard mask material.

As shown in cross-sectional view 1500 of FIG. 15 , in some embodiments,a removal process is performed according to the masking structure 1402to remove peripheral portions of the first and second continuous metallayers (1302, 1304 of FIG. 14 ) to form a capping structure 122 over theactive structure 110 that comprises a first metal layer 124 and a secondmetal layer 326 arranged over the first metal layer 124. In someembodiments, the removal process of FIG. 15 comprises a wet or dryetching process. In some embodiments, an upper surface of the secondmetal layer 326 is narrower than a lower surface of the first metallayer 124 as a residual effect from the removal process of FIG. 15 .

As shown in cross-sectional view 1600 of FIG. 16 , in some embodiments,a thermal annealing process is performed. In some embodiments, thethermal annealing process is performed in a chamber at a temperature ina range of between, for example, approximately 400 degrees Celsius andapproximately 700 degrees Celsius. In some embodiments, after thethermal annealing process, a diffusion region 128 is formed within thetopmost layer 110 t of the active structure 110. In some embodiments,the diffusion region 128 comprises a metal oxide made up of the firstmetal material of the capping structure 122 and oxygen. In some suchembodiments, the first metal material may diffuse into the active layerduring the thermal annealing process and bond with loosely bonded oxygenin the active structure 110 because the first metal material has ahigher affinity for oxygen than metals in the active structure 110.Thus, the capping structure 122 aids in reducing defects (e.g., oxygenvacancies, surface states, weakly bonded oxygen) in the active structure110 to improve performance of the FET FeRAM device.

In some embodiments, after the thermal annealing process, source/draincontacts 118 are formed over the active structure 110 and on either sideof the capping structure 122. In some embodiments, the source/draincontacts 118 are formed within an interconnect dielectric layer 116arranged over the active structure 110 through various steps comprisingdeposition processes (e.g., PVD, CVD, ALD, sputtering, etc.) removalprocesses (e.g., wet etching, dry etching, chemical mechanicalplanarization (CMP), etc.), and/or patterning processes (e.g.,photolithography/etching). In some other embodiments, the source/draincontacts 118 are formed first, and then the interconnect dielectriclayer 116 is formed between the source/drain contacts 118 and over theactive structure 110.

In some embodiments, the interconnect dielectric layer 116 comprises,for example, a nitride (e.g., silicon nitride, silicon oxynitride), acarbide (e.g., silicon carbide), an oxide (e.g., silicon oxide),borosilicate glass (BSG), phosphoric silicate glass (PSG),borophosphosilicate glass (BPSG), a low-k oxide (e.g., a carbon dopedoxide, SiCOH), or the like. In some embodiments, the source/draincontacts 118 comprise, for example, aluminum, tungsten, copper,tantalum, titanium, or some other suitable conductive material.

Further, in some embodiments, voltage terminals are coupled to the gateelectrode 106 and the source/drain contacts 118. In some embodiments,the capping structure 122 is grounded. In other embodiments, the cappingstructure 122 is not grounded or coupled to any voltage terminal.Nevertheless, in some embodiments, the overall structure formed in FIG.16 is a thin film transistor (TFT) that is also a field effecttransistor (FET) ferroelectric random access memory (FeRAM) device. Insome such embodiments, when sufficient signals (e.g., current, voltage)are applied to the source/drain contacts 118 and the gate electrode 106,channel regions may be formed in the active structure 110 to read memoryfrom or write memory to the gate dielectric layer 108. In someembodiments, the capping structure 122 arranged over the activestructure 110 and the cocktail layer 112 arranged directly on the gatedielectric layer 108 aid in reducing defects (e.g., surface states,oxygen vacancies, weakly bonded oxygen) in the active structure 110 andthus, the channel regions to increase switching speeds and reliabilityof the overall FET FeRAM device.

FIGS. 17-20 illustrate cross-sectional views 1700-2000 of somealternative steps for forming the capping structure 122 over the activestructure 110.

As shown in cross-sectional view 1700 of FIG. 17 , in some embodiments,the interconnect dielectric layer 116 is first formed over the activestructure 110.

As shown in cross-sectional view 1800 of FIG. 18 , in some embodiments,the interconnect dielectric layer 116 is patterned to form an opening1802 within the interconnect dielectric layer 116 to expose the activestructure 110. In some embodiments, the opening 1802 in the interconnectdielectric layer 116 is formed by various steps of deposition processes(e.g., PVD, CVD, ALD, sputtering, spin-on, etc.), patterning processes(e.g., photolithography/etching), and removal processes (e.g., wetetching, dry etching).

As shown in cross-sectional view 1900 of FIG. 19 , in some embodiments,the first metal layer 124 is formed within the opening 1802 of theinterconnect dielectric layer 116. In some embodiments, the first metallayer 124 partially fills the opening 1802, whereas in some otherembodiments, the first metal layer 124 completely fills the opening1802. In some embodiments, the first metal layer 124 is formed by adeposition process (e.g., PVD, CVD, ALD, sputtering, etc.) followed by aremoval process (e.g., etching, CMP).

As shown in cross-sectional view 2000 of FIG. 20 , in some embodiments,the second metal layer 326 is formed over the first metal layer 124within the opening (1802 of FIG. 19 ) to form the capping structure 122over the active structure 110. In some embodiments, the thermalannealing process is performed to form the diffusion region 128 of theactive structure 110. Then, in some embodiments, the source/draincontacts 118 are formed within the interconnect dielectric layer 116.

In some other embodiments, prior to forming the second metal layer 326over the first metal layer 124, the interconnect dielectric layer 116 ispatterned to form openings for the source/drain contacts 118. In someembodiments, the second metal material is then formed within theopenings for the source/drain contacts 118 and in the opening (1802 ofFIG. 19 ) of the interconnect dielectric layer 116 to form thesource/drain contacts 118 and the second metal layer 326. In suchembodiments, the source/drain contacts 118 and the second metal layer326 may comprise the second metal material. Further, in some suchembodiments, the thermal annealing process to form the diffusion region128 may be performed before or after the deposition of the second metalmaterial.

In some embodiments, because the capping structure 122 is formed withinthe opening (1802 of FIG. 19 ) of the interconnect dielectric layer 116,the capping structure 122 may have a topmost surface that is wider thana bottommost surface. Further, in some embodiments, because the cappingstructure 122 is formed within the opening (1802 of FIG. 19 ), lessdamage from removal processes may occur to the topmost layer 110 t ofthe active structure 110 compared to other embodiments, wherein thefirst metal layer 124 is formed prior to forming the interconnectdielectric layer 116 as illustrated in, for example, FIGS. 13-16 .

Nevertheless, in some embodiments, the capping structure 122 aids inreducing defects (e.g., surface states, oxygen vacancies, weakly bondedoxygen) in the active structure 110 to improve switching speeds andreliability of the overall FET FeRAM device.

FIG. 21 illustrates a flow diagram of some embodiments of a method 2100of forming a FET FeRAM device comprising a capping structure arrangedover an active structure to reduce defects in the active structure andincrease switching speeds and reliability of the overall FET FeRAMdevice.

While method 2100 is illustrated and described below as a series of actsor events, it will be appreciated that the illustrated ordering of suchacts or events are not to be interpreted in a limiting sense. Forexample, some acts may occur in different orders and/or concurrentlywith other acts or events apart from those illustrated and/or describedherein. In addition, not all illustrated acts may be required toimplement one or more aspects or embodiments of the description herein.Further, one or more of the acts depicted herein may be carried out inone or more separate acts and/or phases.

At act 2102, a gate electrode is formed over a substrate. FIG. 7illustrates a cross-sectional view 700 of some embodiments correspondingto act 2102.

At act 2104, a gate dielectric layer is formed over the gate electrodeand comprises a ferroelectric material. FIG. 8 illustrates across-sectional view 800 of some embodiments corresponding to act 2104.

At act 2106, an active structure is formed over the gate dielectriclayer. FIG. 10A illustrates a cross-sectional view 1000A of someembodiments corresponding to act 2106.

At act 2108, a first metal layer is formed over the active structure.FIG. 13 illustrates a cross-sectional view 1300 of some embodimentscorresponding to act 2108.

At act 2110, peripheral portions of the first metal layer are removed toform a capping structure over the active structure. FIG. 15 illustratesa cross-sectional view 1500 of some embodiments corresponding to act2110.

At act 2112, a source contact and a drain contact are formed over theactive structure, wherein the capping structure is arranged laterallybetween the source contact and the drain contact. FIG. 16 illustrates across-sectional view 1600 of some embodiments corresponding to act 2112.

Therefore, the present disclosure relates to a method of forming anactive structure over a ferroelectric layer and a capping structure overthe active structure to reduce defects and optimize charge mobility inthe active structure to increase switching speeds and reliability of theoverall FET FeRAM device.

Accordingly, in some embodiments, the present disclosure relates to anintegrated chip, comprising: a gate electrode arranged over a substrate;a gate dielectric layer arranged over the gate electrode comprising aferroelectric material; an active structure arranged over the gatedielectric layer and comprising a semiconductor material; a sourcecontact and a drain contact arranged over the active structure; and acapping structure arranged over the active structure and between thesource contact and the drain contact, wherein the capping structurecomprises a first metal material.

In other embodiments, the present disclosure relates to an integratedchip comprising: a gate electrode arranged over a substrate; a gatedielectric layer arranged over the gate electrode, wherein the gatedielectric layer comprises a ferroelectric material; an active structurearranged over the gate dielectric layer; a source contact and a draincontact arranged over the active structure; and a capping structurearranged over the active structure and between the source contact andthe drain contact, wherein the capping structure comprises a first metalmaterial that has a higher affinity for oxygen than metals in the activestructure.

In yet other embodiments, the present disclosure relates to a methodcomprising: forming a gate electrode over a substrate; forming a gatedielectric layer comprising a ferroelectric material over the gateelectrode; forming an active structure over the gate dielectric layer;forming a first metal layer over the active structure; removingperipheral portions of the first metal layer to form a capping structureover the active structure; and forming a source contact and a draincontact over the active structure, wherein the capping structure isarranged laterally between the source contact and the drain contact.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An integrated chip, comprising: a gate electrodearranged over a substrate; a gate dielectric layer arranged over thegate electrode and comprising a ferroelectric material; an activestructure arranged over the gate dielectric layer and comprising asemiconductor material; a source contact and a drain contact arrangedover the active structure; and a capping structure arranged over theactive structure and between the source contact and the drain contact,wherein the capping structure comprises a first metal material anddirectly contacts a diffusion region of the active structure, andwherein the diffusion region comprises the first metal material and afirst material of the active structure.
 2. The integrated chip of claim1, wherein the active structure comprises a stack of cocktail layersalternating with first active layers, wherein the cocktail layerscomprise a mixture of the first material and a second material, whereinthe first active layers comprise a third material different than thefirst and second materials, wherein a bottommost layer of the activestructure is one of the cocktail layers, and wherein a topmost layer ofthe active structure is arranged over the stack of cocktail layersalternating with first active layers and comprises the first material.3. The integrated chip of claim 1, wherein the active structurecomprises a stack of first active layers comprising a first metal oxidematerial, second active layers comprising a second metal oxide material,and third active layers comprising a third metal oxide material.
 4. Theintegrated chip of claim 1, wherein the capping structure comprises afirst layer comprising the first metal material and a second layerarranged over the first layer and comprising a second metal material. 5.The integrated chip of claim 1, wherein the capping structure isgrounded.
 6. The integrated chip of claim 1, wherein the first metalmaterial has a higher affinity for oxygen than materials of the activestructure.
 7. The integrated chip of claim 1, wherein the activestructure comprises a lower portion comprising a mixture of the firstmaterial, a second material, and a third material, and wherein theactive structure comprises an upper portion arranged over the lowerportion and comprising the first material.
 8. An integrated chipcomprising: a gate electrode arranged over a substrate; a gatedielectric layer arranged over the gate electrode, wherein the gatedielectric layer comprises a ferroelectric material; an active structurearranged over the gate dielectric layer; a source contact and a draincontact arranged over the active structure; and a capping structurearranged over the active structure and between the source contact andthe drain contact, wherein the capping structure comprises a first metalmaterial that has a higher affinity for oxygen than metals in the activestructure.
 9. The integrated chip of claim 8, wherein the activestructure comprises a first material, a second material that isdifferent than the first material, and a third material that isdifferent than the first and second materials, wherein the firstmaterial and the second material directly contact the gate dielectriclayer, wherein the third material is spaced apart from the gatedielectric layer by the first and second materials, and wherein thecapping structure directly contacts the first material and not thesecond or third materials.
 10. The integrated chip of claim 8, whereinthe capping structure comprises a first layer comprising the first metalmaterial and a second layer comprising a second metal material andarranged over the first layer.
 11. The integrated chip of claim 10,wherein the first layer directly contacts a diffusion region of theactive structure, and wherein the diffusion region comprises the firstmetal material and oxygen.
 12. The integrated chip of claim 8, whereinthe capping structure comprises a mixture of the first metal materialand a second metal material.
 13. The integrated chip of claim 8, furthercomprising: an interconnect via arranged below and coupled to the gateelectrode; a first interconnect wire arranged over and coupled to thesource contact; a second interconnect wire arranged over and coupled tothe drain contact; and an interconnect dielectric structure surroundingthe interconnect via, the first interconnect wire, the secondinterconnect wire, the source contact, the drain contact, and thecapping structure.
 14. The integrated chip of claim 8, wherein thecapping structure is grounded.
 15. The integrated chip of claim 8,wherein a topmost layer of the active structure comprises gallium oxide,and a bottommost layer of the active structure comprises a mixture ofgallium oxide and indium oxide.
 16. A method comprising: forming a gateelectrode over a substrate; forming a gate dielectric layer comprising aferroelectric material over the gate electrode; forming an activestructure over the gate dielectric layer; forming a first metal layerover the active structure; removing peripheral portions of the firstmetal layer to form a capping structure over the active structure; andforming a source contact and a drain contact over the active structure,wherein the capping structure is arranged laterally between the sourcecontact and the drain contact.
 17. The method of claim 16, wherein theforming of the active structure comprises: forming a cocktail layer overthe gate dielectric layer by activating two precursors at one time suchthat the cocktail layer comprises a mixture of a first material and asecond material; forming a first active layer over the cocktail layercomprising a third material different than the first and secondmaterials; and repeating the forming of the cocktail layer and the firstactive layer to form a stack of cocktail layers and first active layersalternating with one another over the gate dielectric layer; and forminga topmost active layer comprising the first material over the stack ofcocktail layers and first active layers.
 18. The method of claim 16,further comprising: forming a second metal layer over the first metallayer; and removing peripheral portions of the second metal layer,wherein the capping structure comprises the first and second metallayers.
 19. The method of claim 16, wherein the first metal layer isformed using solid precursors and an atomic layer deposition process.20. The method of claim 16, further comprising: performing a thermalannealing process after the formation of the first metal layer andbefore forming the source and drain contacts.